The broadcast is still totally free though. And if you get Comcast and use their X1 box you already have it.
The Phillies don't really get a say. This is what Comcast pays the teams money for, to be able to drive eyeballs to whatever outlet they choose, depending what the contract allows (they also get to set the blackout rules, essentially).
And if you're a cord-cutter, this is actually an upgrade. The person who doesn't have cable but also can't stream Phillies games (which require either a cable subscription or to be out-of-area) can actually do so for these three games. It's definitely a trial balloon. But if we agree the sport needs to reach younger fans, these Amazon/Facebook/YouTube/Peacock broadcasts are meeting them where they are.
The bigger question is still what the future of NBCSN Philly (and, apparently, San Francisco) is. The Portland network lost their Blazers deal and is folding. In Philly they have three teams, and part-ownership by the Phillies (and de facto ownership by the Flyers) but all indication is NBC wants out of the business (having folded the national sports network) and/or wants it to be streaming-driven. And if that's where the viewers and revenue is you can't blame them or the Phillies for trying it. That doesn't mean they know what they are doing, of course.
I imagine the uproar was way worse when games went from free TV to cable in the first place.